Posted
by
Soulskill
on Saturday September 14, 2013 @08:08PM
from the useless-physics-trivia dept.

New submitter TaleSlinger sends this quote from Nature:
"Afshordi's team realized that if the bulk universe contained its own four-dimensional (4D) stars, some of them could collapse, forming 4D black holes in the same way that massive stars in our Universe do: they explode as supernovae, violently ejecting their outer layers, while their inner layers collapse into a black hole. In our Universe, a black hole is bounded by a spherical surface called an event horizon. Whereas in ordinary three-dimensional space it takes a two-dimensional object (a surface) to create a boundary inside a black hole, in the bulk universe the event horizon of a 4D black hole would be a 3D object — a shape called a hypersphere. When Afshordi's team modeled the death of a 4D star, they found that the ejected material would form a 3D brane surrounding that 3D event horizon, and slowly expand. The authors postulate that the 3D universe we live in might be just such a brane — and that we detect the brane's growth as cosmic expansion. 'Astronomers measured that expansion and extrapolated back that the Universe must have begun with a Big Bang — but that is just a mirage,' says Afshordi."

Arguably... to enter the universe inside a blackhole; you have only to enter the event horizon, and merge with it.

Once you merge with the event horizon; you can never leave the black hole or ever be visible to an outside observer again.
Also; you will get squashed into 2 dimensions, and your particles will be scrambled ---- so although the matter that comprises you merges with the universe inside the blackhole: your physical body does not survive.

Physicists cannot say what happens to your immortal soul --- whether it escapes the pull; or whether it too becomes entrapped in the event horizon of that featureless pocket universe for the rest of eternity.

You know, like the theory that the entire universe is a gigantic is a simulation similar to the matrix. There was a very elaborate, college-funded experiment to test that actually (as seen on slashdot)

Funny, but also Insightful?
Turtles all the way down, or turtles all the way up?
If we inhabit the 3D manifold that resides in a black hole within a 4D bulk universe, and observe 3D black holes (with a 2D event horizon), does this imply 1D black holes inside of the black holes that we observe (with 0D black holes inside...). Is the 4D bulk universe a black hole in a 5D hyper-bulk universe within a 6D...
Is there a physicist in the house that can shed more light on this than the article/paper?

I'm trying to decide whether this makes any more sense than a square circle. 3D surface is a contradiction in terms. A surface is 2 dimensional by definition.

The term "surface" normally refers to a two-dimensional shape in 3D space, but it can be generalized to any number of dimensions (a hypersurface). One example would be a hypersphere (x**2 + y**2 + z**2 + w**2 = 1), which has three orthogonal directions of movement along the hypersurface and encloses a four-dimensional space. Movement tangent to the hypersphere it would seem like movement in normal 3D Euclidean space, except that if you travel far enough in any direction you'll eventually end up back where you started.

Once something has passed the edge of the visible universe it is effectively lost to us

Only until we build a bigger telescope.

It's not a matter of how large or sensitive the telescope is; if something is far enough away, the expansion of the space between the object and ourselves causes the distance between us to increase faster than the speed of light, meaning light from the object can never reach us. Once something reaches that distance it's cut off from us for good (or at least as long as the universe continues to expand).

It's not really the same because anything that collides with a black hole will cease to exist.... Even if the collapsed star's gravity did not stop the photons from exiting it would effectively vanish out of existence.

These are one and the same thing. Black holes are not particularly special; the event horizon isn't some solid barrier things crash into. It's merely the point of no return, beyond which escape velocity exceeds the speed of light. Objects which enter a black hole "cease to exist" in exactly the same sense as objects which pass beyond the visible universe: any effect involving the object would need to propagate faster than the speed of light to reach us.